Typically, in the manufacturing of plastic spectacle lenses, a spectacle lens blank produced by injection molding of plastic, also known as a “blank”, is used, that has a standardized finished outer surface with a convex shape, for example a spherical or progressive shape. The outer shape in conjunction with the usually concave inner or prescription surfaces produce a desired optical effect by attaining a machined spherical, aspherical, torical, atorical, progressive or freeform geometry (e.g. varifocal lenses). After blocking the spectacle lens blank with its outer surface onto a block piece, the typical conventional procedure for the processing of the inner surface includes, a milling or lathe process for the production of the optically active shape, in general followed by a fine grinding or polishing process in order to achieve the necessary surface quality.
Suggestions for the manufacture of the optically active shape of plastic spectacle lenses have included pure milling machines, specifically for the rough processing of the spectacle lenses; pure fast-tool lathes with a lathe tool that can be highly dynamically moved for the fine processing of the spectacle lenses, either by linear reciprocation or rotation so that lens surfaces not symmetrical with respect to rotation can be generated in the lathe process; and also combined milling and lathe machines with a combined milling and lathe tool; or separate milling and (linear or rotary working) lathe units. The spectacle lenses can be processed either in series with one and the same spectacle lens is milled and subsequently lathe machined in the work space of the machine or parallel where different spectacle lenses are worked on at the same time in the work space of the machine, in which one is milled and the other is lathe machined.
A series working combined milling and lathe machine is known from the state of the art that includes in general the following subassemblies: a work piece spindle that rotatably drives the work piece about a work piece rotation axis, at least one processing unit that has a tool that machines the work piece that is retained on the work piece spindle; and an adjusting mechanism that generates a relative movement between the work piece spindle and the tool, in order to enable either loading, unloading or processing of the work piece.
More accurately, the known machine has a milling unit with a milling spindle and a lathe unit with two fast-tool arrangements in parallel arrangement on one side of a work space. The adjusting mechanism that is provided on the opposite side of the work space. The adjusting mechanism is formed by a cross slide arrangement that supports the work piece spindle. The work piece spindle can move the work piece relative to the processing units in a parallel direction along an X-axis and in a towards and away direction along a Y-axis. Admittedly, this machine concept has proven itself already in practice and is on the market under the name VFT Ultra, produced by Satisloh AG.
In the manufacturing of plastic spectacle lenses according to prescription, considerable parts of the work piece are machined while supplying large amounts of coolant, which makes it essential to isolate or enclose the work space sufficiently and to ensure unhindered removal of waste chips. In addition, unpleasant vapors may be formed during the machining of certain high index materials that should be removed by suction and filtered.
A stainless steel shield is provided in the above described machine to shield against spray and for providing encapsulation of the work space. The shield is relatively large and expensive because the X-axis is relatively long and the shield casing has to accommodate the movement of the work piece spindle along the long X-axis. An elongated opening is provided in the shield casing to accommodate the motion and access to the work piece spindle. This opening is closed by a combined slide and roll cover that cooperates with wipers on the casing side. As such, this shield compromises the machine efficiency and added expense of the machines.